The Epidemiology of Sudden Oak Death Disease Caused by Phytophthora ramorum in a Mixed Bay Laurel-Oak Woodland Provides Important Clues for Disease Management.

Matteo Garbelotto,Todd W. Osmundson,Melina Kozanitas,Margaret R. Metz,Maria Socorro Serrano

doi:10.3390/pathogens11020250

Abstract

Epidemiological models are important for the understanding of disease progression in plants and for the design of control strategies. Phytophthora ramorum, the pathogen responsible for the disease known as Sudden Oak Death, causes lethal infection on several oaks but relies on California bay laurels for transmission. Here, repeated surveys of bay laurels and oaks indicated that bay laurel disease incidence was positively correlated with rainfall, bay laurel density, and an eastern aspect, and negatively correlated with bay laurel basal area. Oak infection only occurred in years when rainfall was higher than the 30-year average, and although infection rates were greater among larger trees, mortality was greater among smaller trees. Additionally, larger oaks closer to infected bay laurels exhibited greater infection rates. Disease incidence differed among sites, and only a fraction of bay laurels were disease superspreaders, while even fewer individuals were refugial trees harboring active infections during dry periods. Based on this study, reducing bay laurel density in denser stands and the number of superspreaders or refugial trees in less dense stands may reduce disease incidence. However, the selective removal of bay laurel trees 0–10 m from oaks is likely to be more effective in preventing infection of specific oaks.

Highlights

The role of pathogen transmission and host competence heterogeneity at individual tree- and population-level scales is increasingly recognized as an important driver of plant disease epidemics [1,2,3,4]
Sites where superspreaders are present might serve as hotspots for disease spread and sites containing refugial trees could become starting points for future outbreaks due to a pathogen’s ability to survive in these inoculum reservoirs during climatically unfavorable periods
Likewise, knowing the location and the characteristics of sites where superspreading individuals and/or refugial hosts are likely to occur would help us to better understand the epidemiology of a disease and to identify effective control strategies. This is true for a disease such as Sudden Oak Death (SOD), which is the topic of this study, characterized by a large, fragmented, range, and by the cryptic or quasi-cryptic infection status of many plant hosts [16]

Summary

Introduction

The role of pathogen transmission and host competence heterogeneity at individual tree- and population-level scales is increasingly recognized as an important driver of plant disease epidemics [1,2,3,4]. Likewise, knowing the location and the characteristics of sites where superspreading individuals and/or refugial hosts are likely to occur would help us to better understand the epidemiology of a disease and to identify effective control strategies. This is true for a disease such as Sudden Oak Death (SOD), which is the topic of this study, characterized by a large, fragmented, range, and by the cryptic or quasi-cryptic infection status of many plant hosts [16]

Methods

Results

Conclusion